Multiple foreign key problem - 3NF

Hi, Let's say you have 3 tables A, B and C. B inherits from A and uses A.id as a foreign key. Then, C inherits from B and uses B.id as a foreign key. However, sql dbm interface adds A.id and B.id to C as a foreign keys. In this case, I just want to have a relationship between B and C and just B.id as a foreign key in C. No need for A.id in C. I can reach A through B from C. I think this also violates 3NF rule.

table A{

id

}

table B{

id PK

a_id FK

}

table C{

id PK

b_id FK

a_id FK --> this should be an option in a relationship not compulsory

}